Gravity gradiometers are sensing systems designed to detect the gradient, or spatial derivative, of the gravitational field of an object. As one example, an object passing near a gravity gradiometer may exert a changing gravitational force on the gradiometer due to the movement of the object near the gradiometer. The gradiometer detects the temporal evolution of the spatial derivative of the gravitational field of the object as it passes by. This temporal evolution may be used to determine the mass, density, velocity, or other related properties of the object.
Conventional gravity gradiometers typically use one or more opposing pairs of accelerometers to detect the gradient of a gravitational field along an axis. In particular, a difference in sensed acceleration between each of the pairs of accelerometers is used as an indicator of the difference in the gravitational force between two points along the axis of the gradiometer. However, these types of gravity gradiometers are often incapable of detecting small gravity gradients, and surrounding noise often diminishes the quality of the signal from the gravity gradiometer.
Due to this low sensitivity, gravity gradiometer measurements using conventional systems are often limited to the detection of signals from very large masses for applications that permit low resolution measurements. To isolate the gravity gradiometer from surrounding noise and increase sensitivity of the unit, some conventional gravity gradiometers have attempted to use complex active isolation systems to stabilize the gravity gradiometer. In other gradiometers, temperature stabilization systems are applied to the pairs of accelerometers to try and achieve more accurate scale factor matching. For example, superconducting gravity gradiometers implement large cryogenic systems to stabilize the accelerometers at low temperatures, thereby trying to improve sensitivity. In this way, various conventional gravity gradiometers often achieve very low sensitivity or, in order to increase sensitivity, often become large, unwieldy, and expensive sensing systems.